For data exchange between a fixed computer on the ground and a mobile computer located on board a vehicle, document WO 2005/022839 A1 discloses an architecture using an intermediate communication infrastructure suitable for establishing a wireless link with a mobile gateway which is located on board the vehicle and to which the mobile computer is connected. The communication infrastructure comprises a plurality of base stations. Each base station can establish a wireless link with the mobile gateway using radio communication means when the vehicle is located within the coverage cell of said base station. The different base stations are mutually aggregated and connected to an IP network via an intermediate gateway (“foreign agent”). Once the wireless link is established, the intermediate gateway assigns an IP address on the IP network to the mobile gateway and thereby creates an access point to the IP network. The known architecture also comprises a main gateway which makes it possible to route the IP datagrams to the mobile computer via the appropriate intermediate gateway. In uplink communication, an IP datagram is routed directly to the fixed computer.
In this known architecture, there is only a single intermediate gateway for all the base stations of an individual communication infrastructure. This is the intermediate gateway which configures the logical layer of the communication between the intermediate gateway and the mobile gateway for each new wireless link. The temporal aspect of passing from one cell to another cell of the same infrastructure is not a constraint in this architecture, which has reduced performance levels.
Furthermore, the radio communication means with which a base station is equipped only have a reduced range covering a basic geographical region or cell. Thus, as a juxtaposition of base stations, an infrastructure can only establish a link with a mobile piece of equipment in a highly delimited coverage region corresponding to the different cells.
Moreover, in the coverage region of an infrastructure it is possible for there to be a shadow region where the propagation of the electromagnetic waves is disturbed or blocked by the presence of obstacles between the base station and the vehicle. This is the case for example when a train passes through a tunnel and the link with the base stations of a GSM infrastructure is broken.
To remedy the presence of shadow regions or even the reduced size of the coverage region, a plurality of ground infrastructures are used to cover the entirety of the region within which the vehicle is assumed to have to travel. For example, a mobile piece of equipment which used a first GSM infrastructure in a first country would connect to a second GSM infrastructure available in a second country when crossing the border between these two countries.